The selective adsorption of CO2 from binary mixtures of N2 and CH4 was investigated using a structurally dynamic porous coordination polymer, catena-bis(dibenzoylmethanato)-(4,4‰bipyridyl)nickel (II), ,NiDBM-Bpy‰, as the separation sorbent. A third gas, N2O, was also evaluated that exhibits competitive, non-selective, nearly 1:1 co-adsorption with CO2. The analysis is based on three complementary techniques involving in situ attenuated total reflectance Fourier-transform infrared spectroscopy to probe adsorption of infrared active gases directly in the NiDBM-Bpy pore, gas chromatography to monitor gas composition changes in the headspace above the sorbent bed, and small angle neutron scattering to provide structural information on the porosity changes. These measurement techniques indicated highly selective adsorption of CO2 from CO2/CH4 and CO2/N2 mixtures at 30°C. In contrast, the results for the CO2/N2O system shows the two gases are adsorbed in nearly equal ratios.